The invention concerns a process for continuously determining the moisture content of a spoilable foodstuff, in particular, of grain and processed products of the latter (referred to as "product"), which is moved along a production line as a product stream and passed, at least in part, through a measuring section.
The invention also concerns a device, especially for carrying out the invention process, for continuously determining the moisture content of spoilable foodstuffs, in particular, grain and processed products of the latter, as it is moved through a measuring housing.
In a milling operation, to the present various material characteristics, and in particular moisture content, can only be measured with unsatisfactory precision.
The causes for this lie in a large number of factors. The good itself is to be found in two extreme conditions, namely on the one hand at rest, stored in silos, and on the other hand in flow from processing stage to processing stage. It is particularly difficult to obtain exact material values in a continually moving product, and therefore in practice, the laboratory method performed on samples has been used for determination of the exact value. To determine exact material values of a large quantity of a pourable good regularly entails the testing of many samples and the statistical evaluation of the result. Manipulation of the sample taking mechanism is awkward, particularly for large silo cells, since to the extent possible, samples must be drawn from various places within the silo, while within silos very high pressures and compressions are usual.
A further difficulty lies in the fact that the product moisture can vary between relatively wide extreme values, which has a direct influence on the product dry volume, and also, for example, the density and electrical conductivity.
In the mill, generally various grain types are mixed together. However, it is not necessary that the mixing of the various sorts be performed very precisely, since in the subsequent processing stages a repeated mixing of the individual fractions can be performed if required. The individual type fractions have various physical properties among them, and in particular the bulk weight is different, and usually the product moisture content as well.
Constrained by these problematics, the measurement by sampling of individual physical quantities has remained an unsolved problem, and this applies quite particularly to the exact determination of the water content in the product.
In a familiar process for determination of the water content in grain, the grain is removed by a mechanism from a product stream in a batch or quasi-continuous operation, and poured in a certain weighed quantity into a measurement container. The measurement container is in part constituted as a condenser, and a measurement is made by determination of an electrical value in the form of the capacitance of the condenser constituted by the container with the product, and in evaluation is converted to the quantity of water present in the sample. This instrument reflects the actual water content of the measurement sample, but it is questionable with this method, whether the measurement values are representative of the entire product stream.
If the product is to be moistened to a particular water content, the product throughput must be received in a subsequent continuously operating weighing system, and the necessary supplemental water quantity computed and added. Although this system is employed relatively frequently in practice, it may often be insufficient for the requirements in a mill. If the moistures or water contents produced are namely determined by an exact laboratory method, for example, in a drying oven, variations in the relative moisture content of frequently up to half a percent, and sometimes up to one percent are discovered. The electrical measurement method here described has the particular failing that the values determined are very much type dependent. To exclude this factor, calibration must be performed for each grain type before beginning measurement. For transparent reasons, this calibration is useless in the case of a mixing of more than one type, if the mixing ratio itself is not precisely known or precisely defined.
Appearing especially critical is the question of the water content, with regard to whether the water content has changed soon or long before the measurement. The electrical conductivity is affected by each of the parameters cited.
In milling to the present, in the majority, only the traditional laboratory measurement methods have been given confidence, which, however, has limited a further automation of mills, since such decisive parameters as the exact throughput quantity, the exact moisture content, or even the exact level of the good could not be monitored with sufficient confidence.
Other measuring processes have not found any substantive application in the milling filed. Measuring processes with microwaves, gamma-rays and the like are not being considered due to the risks inherent in the rays. Other measuring processes on the other hand are suitable for dead materials, textiles, paper, sand and the like and are precluded from grain which is a living substance, since the measuring results are totally unusable.
A part of the invention is to overcome the known deficiency in the state of the art, in particular to find a new process for determination of physical quantities, in which the values determined for as large as possible a quantity of product and to as high as possible a precision are made available. The process should render unnecessary any constant recalibration both with respect to special grain types, and with respect to short and long term behavior. The solution is to be simple and economical to manufacture, and be operable even by personnel with little training.
In relation to the process, the solution provided by the invention is distinguished by the fact that a pourable average of the product stream is created continuously within the measuring section, and the product moisture content of this product average is measured electrically on a continuous basis.
In relation to the device, the solution provided by the invention is distinguished by the fact that the measuring housing has a capacitor as a continuous-flow measuring section and a device for continuously controlling the creation of a pourable product average.
It has been shown that the new solution concept has resulted in a substantial step forward in terms of increasing operational reliability. The new invention establishes a new branch for automation of mill operation. On one hand, the new process permits the moisture content of the product to be determined with considerably higher accuracy, and on the other, it makes possible the elimination of moisture as a source of problems, for example, in the exact measurement of flow rates or levels.
One of the central concepts of the invention is found in the interaction of the following factors:
continuous creation of a product average
continuous trickling-type flow of the product
with simultaneous electrical measurement on a continuous basis
The invention suggests first of all that a product average be produced in place of the awkward process employed to date of taking samples and evaluating them individually. In this process the product average should be constantly reformed in a continuous, trickling flow with simultaneous electrical measurement of the product.
The quantity of product measured may actually lie within range from a few percent of the entire quantity of product up to 100 percent, according to the particular situation. In the case of the known process, the fact has been disregarded that the shape and the composition of the measurement sample are just as important as the measuring process itself. With poor sampling, even the best measuring method is rendered unusable. Practice has shown that measurement values obtained according to the principles of the invention even lie within the mean error of the best laboratory methods; moisture content is therefore obviously determined more effectively than in all methods previously used. Moreover, the invention also makes possible a large number of particularly advantageous design elaborations. Thus, according to the invention a relatively large quantity of product, for example, five to ten liters, may be determined with a single measuring process.
It is preferable for an average of the product stream to be produced in the measuring section with respect to time, such that a constant percentage of the product stream is scanned for the determination of moisture content. To extend this concept, this percentage may also be present. In this manner, as mentioned in the beginning, it is possible with unknown mistures to measure a substantially larger proportion of the product, and therefore for the measuring reliability to be increased.
Until today it has not been possible to explain with certainty the influence of individual factors, in particular, the reciprocal influence of the latter.
It is also of particular importance that the movement of the product be retarded in the measuring section in a manner that is free of pressure, that is, occurring by means of gravity alone; that it trickle, as it were, through the measuring section as in an egg timer or hourglass; and that the moisture content be measured during this process.
It is preferable for a first partial flow of product to be passed through the measuring section and a second partial flow through a bypass, each by gravitational force, and to be retarded simultaneously in their downward movement in the section of a measuring housing formed by the measuring section and the bypass, in particular, to be delayed to different degrees in the measuring section and the bypass. It is advisable for the two partial flows to be created on the overflow principle and to be reunited beneath the measuring section in such a manner that a controlled backlog in the measuring section is created in the area where the two partial flows are brought together. The outlet port from the measuring section can be designed as a presetable gate valve in order to bring about the passage of a certain desired percentage of the product through the measuring section. The movement of the product in the bypass is controlled according to another idea, for the purpose of maintaining a constant level in the bypass to ensure a constant product backlog in the measuring section.
The capacitance in the measuring section designed as a measuring capacitor is preferably measured directly, and the values obtained delivered to an electronic evaluator for the determination of the moisture content of the product. It is preferable for the measurement capacitor to be charged to a certain voltage in a first phase, and in a second phase for a reference capacitor to be connected to the measuring capacitor, the measuring capacitor to be discharged into the reference capacitor, and the voltage obtained in this manner to be measured over the reference capacitor and delivered to the electronic evaluator, the two phases being repeated in a cyclical manner, the reference capacitor being discharged during the first phase and the voltage across the reference capacitor being delivered to a reservoir at the end of the second phase. In the reservoir a mean value may also be formed from several measured values for determining the moisture content of the product. Another possible elaboration is for the product to be weighted in the measuring section and and the instantaneous weight value to be determined during the electrical measurement, the product stream in the measuring section being controlled in such a manner that the measuring section remains essentially full at all times.
Problems encountered with extreme product mixtures may be avoided with the simultaneous determination of the product moisture content and the weight of the content of the measuring section. Practice has already established that the invention constitutes a considerable developmental advancement, by virtue of the fact that the two partial streams are reunited forming an enclosed product column, and the product movement is regulated to a constant level in the bypass duct, and since the instantaneous flow rate is determined immediately afterward in a continuous process.
One of the secrets of determining exactly the instantaneous throughput of a product stream, for example, by means of appropriately designed deflection plates, is holding the feed relations constant to the extent possible. It has been found that the solution according to the invention produces ideal conditions for quantitative measurement with deflection plates. With the formation of an enclosed product column, disturbances from spurious air currents, etc., are eliminated very effectively and free of charge.
Using the determined moisture content of the product and the instantaneous flow rate, the amount of water lacking--relative to a desired moisture content value--may be determined to the same degree of accuracy in a computer, and a subsequent device for moistening the product may be immediately adjusted.
At any point in time, a product average is being created. The moisture content of this product average is measured on a continuous basis. The measurement produces a true value by which the addition of water may be controlled directly, as a result of the comparison of desired value and actual value. No oscillation buildup occurs, since a basic problem factor, product inhomogeneity, is eliminated by the averaging process. At the same time, full advantage may be taken of the benefits of the electronic measurement method, which also permits averaging, and it may be practically employed for automatically regulating the wetting of grain. The simultaneity of all the processes in the system gives it an unanticipated precision and reliability, to a degree that far surpasses past practice. All the advantages of forward control (regulation) therefore take effect.
To bring about movement of the product by the effect of gravity alone, the product supply ducts in the measurement housing run essentially in a vertical direction.
It is preferable for the device used to continously control the product average to have a level-regulating mechanism. A bypass is assigned to the measuring section to divert a portion of the product stream, as well as a regulating mechanism for the purpose of adjusting the product in the bypass to a constant level and the product in the measuring section to bring about continuous averaging. Simple construction is achieved by placing the measuring section and the bypass immediately adjacent to each other and connecting them by means of an overflow duct and a common product outlet, and also by the fact that the product inlet of the measuring chamber discharges essentially directly above the measuring section, and the product may be guided, flowing freely, through the overflow duct into the bypass. To retard the product it is also advisable for the invention device to have a throughput-regulating mechanism at the product outlet that is controlled by a level sensor located in the regulating duct, or bypass. The level sensor is preferably executed as a membrane located on the side of the regulating duct, which is preferably connected by pneumatic actuating elements to the overflow-regulating mechanism. Manual actuators are also provided for opening and closing the throughput-regulating mechanism, so that the entire device may be emptied when required.
In its preferred and most frequent application, the invention device is provided with a throughput measuring mechanism, which determines its instantaneous throughput for the purpose of computing the amount of water to be added.
It is also possible to install the invention device directly beneath a storage container, such that the delivery output of the storage container may be regulated by the invention device itself. For this purpose it is preferable for the device to have a throughput regulating loop, with a flow rate regulating mechanism and a throughput measuring instrument, in which the electronic evaluator serves as a comparator for comparing the actual value, supplied by the throughput measuring instrument, to the desired value, supplied by a corresponding desired value control unit, and adjusts the flow rate regulating mechanism to maintain the desired value. The two last-named applications make possible ideal conditions for continuously measuring the flow rate of the product. In both cases the continuous flow rate measuring device receives a constant stream of product without spurious air disruptions, as a result of the enclosed product column created by the backlog.
As a result of the combination of the measurement of moisture content according to the invention and the immediately following continuous measurement of product quantity, a subsequent device for wetting or drying the grain can be controlled reliably and very accurately by an electronic evaluator and a second computer, which has not been possible previously in practice. Another possible elaboration is to design the capacitor arrangement as a balance receptacle, or to support it on pressure pickups, so that the balance signal can be processed to determine the settled apparent density of the product within the measuring section.
A further idea for constructional elaboration is for the measuring section to be designed within a measuring chamber in the measurement housing. For this purpose a vertical section of the outer wall of the measuring chamber is designed as a first capacitor plate, and a second capacitor plate is located inside the measuring chamber.
The invention will now be explained in further detail by means of several exemplary executions.